Background: It is significant to maintain the safety and reliability of nuclear engineering materials under a neutron irradiation environment. Purpose: This paper aims to investigate the irradiation damage mechanisms of CLAM

F82H and ?-Fe under the bombardment of neutrons

protons and heavy ions respectively with the aspects of material displacement damage rate and impurities deposition. Methods: The model of material damage under irradiation of reactor was established using the Monte Carlo package Geant4. Results: Irradiation damage caused by neutrons was mainly displacement damage. The distribution of displacement damage caused by protons and heavy ions corresponded to Bragg peak curve

whose incident depth and damage area were concentrated in the surface of material. 14.67-MeV protons had an incident depth of 512 ?m while 0.82-MeV 3He ions were 2.1 ?m only. Conclusion: The damage forming mechanism of metal engineering materials under extreme irradiation environment was systematically analyzed

which provided a theoretical basis for further research of material changes of macroscopic properties and microstructure after irradiation. Abstract